There are numerous systems in which a plurality of air streams are employed in operation of the system. For example, a number of different air streams are used in operating a powder spray system. Typically, powder spray systems include a powder pump for transporting air entrained powder through a pneumatic conveyor line to a powder spray gun. Within the pneumatic conveyor line is a low pressure venturi pumping chamber. This chamber is intersected by a powder supply passage through which powder is supplied (i.e., sucked) from a fluidized bed of powder created by a fluidizing air stream. In order to meter or control the rate of flow of powder from the fluidized bed into the venturi pumping chamber, such pumps ordinarily further include a metering or atomizing air stream which injects a controlled flow of air into the powder supply passage. This atomizing air flow controls the amount of air which is mixed with the powder entering the venturi chamber to thereby adjust the powder/air mixture reaching the delivery air stream.
A powder spray system may thus have three different air streams to be controlled in operation of the system, namely, the fluidizing air stream, the atomizing air stream, and the delivery air stream. All three air streams may operate at different pressures, all of which interact to determine the powder flow rates. The flow rates of the air streams are individually adjustable to compensate for such factors as the type of powder being sprayed, the substrate being sprayed, the type of gun being used and the like. It is therefore important that the air pressure for each of these air streams is capable of variation to independently adjust each of the air flow rates.
One way to control the air stream air pressure values in an electrostatic powder system has been to put a manually operated valve or pressure regulator in each of the air flow lines to independently set the air pressures for each of the different air streams. Use of such manually operated air stream controls have a number of drawbacks, foremost of which is the fact that they cannot be used in any system which is to be fully automated. An operator must consequently be present to manually set or adjust each of the various regulators.
At least one system has been devised in which a number of solenoid operated air regulators are located in each air stream line. Each regulator in a particular air stream is manually set to a different flow rate, i.e., air pressure value. In operation, one regulator in a series is remotely actuated to provide the desired flow rate in that particular air stream. The problem with this type of system is of course in the number of regulators which are required to provide the desired flow rate variability, which results, among other things, in an increase in the size of the regulator system as well as an increase in its cost.
It is also known to use an electronic system to monitor a plurality of air pressures in a powder spray system as well as to variably regulate the individual air streams. Although such an electronic system has the ability to provide variable flow rate regulation of the individual air streams, and do so remotely from the powder pump, the electronic system suffers serious drawbacks in terms of the size of the regulator system as well as its cost, with the expense of the system perhaps being the most significant factor.